Scince when did a car show off ever get a girl? =P
The most dangerous thing they do all day is sit in a chair and try to look dangerous...
On an interesting note the c240 has 168 horsepower, that's about as much as a Ford FOCUS... the SLK230k has 201 horsepower, that's base Mustang level. You do the math kid.
My advice would be to go for the SLK, but try to find one in black...
If you're in the CA area get This baby
It shows you have some style.
Also have you considered a Porsche Boxter? They can be had allong the same lines as a SLK230, are MUCH faster, and nicer and preform well... finding one might be a bit of a pain, but you WON'T regret it.
There's one near you for sale... but it's a 97 I'd get a 99, it's only a few hours dive, you could get it over a weekend. Just car pool with your parents and drive the car back.